1. 10 June 2006MICE Collaboration Meeting CM-151 Can MICE Solid and Liquid Absorbers be Characterized to better than 0.3 Percent? Michael A. Green 1, and Stephanie Q. Yang 2 1. Lawrence Berkeley Laboratory 2. Oxford University Physics Department

2. 10 June 2006MICE Collaboration Meeting CM-152 Ionization Cooling in MICE Potential ionization cooling materials for use in MICE are given in the table below. LH 2 is the best ionization cooling material; LHe is next best. In general the solid absorbers are easier to characterize than the liquid absorbers.

3. 10 June 2006MICE Collaboration Meeting CM-153 What does one need to know in order to simulate the absorber? One needs to know what the absorber is made of as a function of its R and Z coordinates. One needs to know the physical boundaries of the absorber material (liquid or solid). One needs to know the boundaries as a function of absorber T and P. One needs to know the density of the absorber material as a function of the absorber T and P. The absorber content, boundaries and density must be known to better than ±0.2 percent.

4. 10 June 2006MICE Collaboration Meeting CM-154 MICE Solid Absorber Characterization It is difficult to get uncontaminated blocks of lithium hydride. The material content and density are uneven across the block. LiH must be encapsulated. Aluminum, a common encapsulation material, reacts with LiH to form a lithium aluminum hydride. LiH is difficult to characterize to ±0.3 percent because of unknown and uneven material content as well as uneven density. Lithium must be encapsulated. Lithium can be cast into an aluminum box. It is probable that lithium can be characterized to ±0.2 percent.

5. 10 June 2006MICE Collaboration Meeting CM-155 Solid Absorbers Continued Be, Al, and Mg can be machined and they have uniform properties. They can be characterized to much better than ±0.1 percent. Of the plastics, polystyrene is one of the best. It has a uniform density, and it is easily machined. It can be characterized to much better than ±0.2 percent. Polyethylene is a candidate for MICE as well. Graphite is reasonably uniform in density and thickness. It can probably be characterized to better than ±0.2 percent.

6. 10 June 2006MICE Collaboration Meeting CM-156 Liquid Absorber Body Cross Section Absorber Vacuum Door Safety Window Absorber Top Tube Absorber Bottom Tube Absorber Body Absorber Thin Window Heat Exchanger Tube Magnet Coil Magnet Mandrel Heat Exchanger Tube to Condenser Magnet He Feed Tube

7. 10 June 2006MICE Collaboration Meeting CM-157 Characterization of Liquid Absorbers The MICE liquid absorber is designed for both liquid hydrogen and liquid helium operation. To characterize a liquid absorber one must know the dimensions of the absorber and the density of the liquid in the absorber to better than 0.3 percent. The absorber dimensions are a function of both temperature and pressure. The density of the liquid is also a function of temperature and pressure. The absorbers will be cooled using a 4 K cooler. The cooler capacity is 1.5 W at 4.2 K and up to 20 W at 20 K while producing 40 W of cooling at 45 K. The heat leak into the liquid absorber will be < 2 W.

8. 10 June 2006MICE Collaboration Meeting CM-158 A 3D View of the Liquid Absorber and its Cooler H 2 Fill Line Absorber Cooler Vent Line Surge Volume Liquid Line Gas Line Liquid Window Absorber Body At 20 K Absorber V = 20.42 liters From 293 K to 20 K (4 K)the absorber shrinks ~0.425 percent in all directions. The absorber body expands as it is pressurized to 1.2 bar. This expansion is quite small (< 0.03 percent) and predictable.

9. 10 June 2006MICE Collaboration Meeting CM-159 Window Deflection under Pressure

10. 10 June 2006MICE Collaboration Meeting CM-1510 Liquid Boundary as a Function T and P

11. 10 June 2006MICE Collaboration Meeting CM-1511 Liquid Boundary as a Function T and P (in the central region) 80 percent of the muons are in this region.

12. 10 June 2006MICE Collaboration Meeting CM-1512 Vapor Pressure LH 2 as a function of T

13. 10 June 2006MICE Collaboration Meeting CM-1513 LH 2 Density as a function of T and P We know the LH 2 density to ±0.3 percent if we know the hydrogen temperature to ± 300 mK.

14. 10 June 2006MICE Collaboration Meeting CM-1514 Vapor Pressure He as a function of T

15. 10 June 2006MICE Collaboration Meeting CM-1515 LHe Saturated Density as a function of T We know the LHe density to ±0.3 percent if we know the helium temperature to ± 20 mK.

16. 10 June 2006MICE Collaboration Meeting CM-1516 Other Factors affecting Liquid Absorber Characterization The depth of the liquid in the absorber and its fill pipes changes the pressure across the window. This pressure change is 240 Pa for H 2 and about 400 Pa for He. The effect on absorber performance is small (<0.01 percent for LH 2 @ 18 K). The 1 to 1.5 W heat leak into the absorber will cause a temperature gradient across the absorber. Simulations suggest that this temperature gradient is less than 200 mK for LH 2 in the worst case. The density change is less than ±0.3 percent for H 2.

17. 10 June 2006MICE Collaboration Meeting CM-1517 Can we predict cooling to ±0.3 percent with the MICE liquid absorbers? The MICE absorber performance can be predicted to ±0.3 percent when it is filled with liquid hydrogen, because we know the hydrogen temperature within ±100 mK. It is not clear that the MICE helium absorber performance can be predicted to ±0.3 percent when it is filled with liquid helium, because it is unlikely that the absolute temperature can be easily measured within ±20 mK. More work is required to find the right temperature sensors.

18. 10 June 2006MICE Collaboration Meeting CM-1518 Window Thickness as a function of R

19. 10 June 2006MICE Collaboration Meeting CM-1519 Window Thickness as a function of R (central region only) 80 percent of the muons are in this region.

20. 10 June 2006MICE Collaboration Meeting CM-1520 Hydrogen Absorber Performance as a function of R

21. 10 June 2006MICE Collaboration Meeting CM-1521 Helium Absorber Performance as a function of R

22. 10 June 2006MICE Collaboration Meeting CM-1522 Concluding Comments The candidate solid absorbers (except LiH) can be characterized to ±0.3 percent. The best materials are Be, polystyrene, graphite, Mg, and Al. A LH 2 absorber can be characterized to ±0.3 percent because we know the density of LH 2 to better than ±0.3 percent. A LHe absorber may not be characterized to ±0.3 percent because we may not know the density of LHe to ±0.3 percent. For many absorber materials, absorber performance can be predicted to ±0.3 percent.